Abstract

Innate immune activation contributes to the transition from nonalcoholic fatty liver to nonalcoholic steatohepatitis (NASH). Stimulator of IFN genes (STING, also referred to Tmem173) is a universal receptor that recognizes released DNA and triggers innate immune activation. In this work, we investigated the role of STING in the progression of NASH in mice. Both methionine- and choline-deficient diet (MCD) and high-fat diet (HFD) were used to induce NASH in mice. Strikingly, STING deficiency attenuated steatosis, fibrosis, and inflammation in livers in both murine models of NASH. Additionally, STING deficiency increased fasting glucose levels in mice independently of insulin, but mitigated HFD-induced insulin resistance and weight gain and reduced levels of cholesterol, triglycerides, and LDL in serum; it also enhanced levels of HDL. The mitochondrial DNA (mtDNA) from hepatocytes of HFD-fed mice induced TNF-α and IL-6 expression in cultured Kupffer cells (KCs), which was attenuated by STING deficiency or pretreatment with BAY11-7082 (an NF-κB inhibitor). Finally, chronic exposure to 5,6-dimethylxanthenone-4-acetic acid (DMXAA, a STING agonist) led to hepatic steatosis and inflammation in WT mice, but not in STING-deficient mice. We proposed that STING functions as an mtDNA sensor in the KCs of liver under lipid overload and induces NF-κB–dependent inflammation in NASH.

Figure 5

Primary hepatocytes and KCs were isolated from C57BL/6 mice. Protein expression of STING (A) was detected in KCs, but not in hepatocytes. The β-tubulin was used as a loading control. Liver sections of mice fed with control chow or HFD were stained for STING (B). The mtDNA (100 ng/ml) from hepatocytes of chow-fed (mtDNA CD) and HFD-fed (mt DNA HFD) mice was added to KCs from WT or STING-deficient mice (Tmem173gt) fed with chow or HFD for 12 hours. The activity of NF-κB (C) was determined by luciferase assay, and mRNA expression of TNF-α (D), IL-6 (E), and IL-1β (F) was determined by RT-PCR. The in vitro experiments were performed 5 times, and each experiment was performed with replicates. *P < 0.05. Statistical significance was determined using 1-way ANOVA followed by Tukey-Kramer multiple comparisons test.